Artist’s impression of the active galactic nucleus. The supermassive black hole at the center of the accretion disk sends a narrow high-energy jet of matter into space, perpendicular to the disc.
Credit: DESY, Science Communication Lab

Physicists have managed to find the origin for the neutrinos that pass through the Earth with at high energy, and have at the same time discovered a new way of studying the universe.

Neutrinos are common but elusive particles. The mass of the neutrino is much smaller than that of the other known elementary particles. We do know that this tiny particle is created by various radioactive decays, including in beta decay of atomic nuclei or hadrons, nuclear reactions such as those that take place in the core of a star or even artificially in nuclear reactors, nuclear bombs or particle accelerator.

The Sun sends enormous numbers of neutrinos in all directions. Each second, about 65 billion (6.5×1010) solar neutrinos pass through every square centimeter on the part of the Earth orthogonal to the direction of the Sun. Since neutrinos are insignificantly absorbed by the mass of the Earth, the surface area on the side of the Earth opposite the Sun receives about the same number of neutrinos as the side facing the Sun.

Scientists have been trying to pinpoint an exact source for high-energy cosmic neutrinos, ghostly elementary particles that travel billions of light years through the universe, flying unaffected through stars, planets and entire galaxies. Now physicists have been able to do just that, that it is indeed possible to locate the sources of neutrinos and have at same time revelead a new way of studying the universe.

An international group of researchers has traced the neutrinos to a so-called blazar with the help of the Ice Cube Observatory in Antarctica. The observatory consists of a network of detectors that are mounted in the Antarctic ice. The detectors can see traces of neutrinos that interact with the atoms in the ice as they pass.

The IceCube Neutrino Observatory under the stars. NSF

Part of the research is to find the neutrinos that do not derive from the direction of the sun or which are created when cosmic radiation comes into contact with the Earth’s atmosphere, but instead, those that are derived from much more distant locations.

“Since neutrinos are a sort of by-product of the charged particles in cosmic rays, our observation implies that active galaxies are also accelerators of cosmic ray particles. More than a century after the discovery of cosmic rays by Victor Hess in 1912, the IceCube findings have therefore for the first time located a concrete extragalactic source of these high-energy particles.”

– Marek Kowalski, the head of Neutrino Astronomy at DESY, a research center of the Helmholtz Association, and a researcher at the Humboldt University in Berlin.

So when such a neutrino was discovered on September 22, 2017, an alarm went off to various telescopes around the world, they were looking for the source from which the neutrino could come from. And for the first time, the telescope in Antarctica managed to find something through measurements of gamma radiation.

With data from NASA’s Fermi’s Large Area Telescope that revealed enhanced gamma-ray emission from a well-known active galaxy. This active galaxy is a type called a blazar, where a supermassive black hole with millions to billions of times the Sun’s mass blasts particle jets outward in opposite directions at nearly the speed of light. Blazars have supermassive black holes at the center of them that rip apart matter into its constituent parts, and then blast subatomic particles off like a laser cannon into space.

An artistic rendering of the IceCube detector shows the interaction of a neutrino with a molecule of ice. The display pattern is how scientists represent data on recorded light. IceCube Collaboration/NSF

This discovery is similar to the recent observations of gravity waves. As with gravitational waves, such successful observations of high-energy neutrinos are a new way of studying the universe. In both cases, it is about being able to perceive phenomena that our traditional telescope for visible light and other electromagnetic radiation cannot see.

 

 

The discovery is hailed as a giant leap forward in a growing field called multimessenger astronomy, where new cosmic signals like neutrinos and gravitational waves are definitively linked to sources that emit light.

“We now have a better understanding of what we should be looking for. This means that we can in future track down such sources more specifically,”

– Elisa Resconi from the Technical University of Munich, whose group contributed crucially to the findings.

References:

The IceCube team et al. Multimenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A. Science July 12, 2018. DOI: 10.1126 / science.aat1378

IceCube Collaboration. Neutrino emission from the direction of the blazar TXS 0506 + 056 prior to the IceCube-170922A alert. Science July 12, 2018. DOI: 10.1126 / science.aat2890